The invention relates to a method of injecting fuel into the combustion chambers of an internal combustion engine having a plurality of cylinders by a main injection process and a variable number of secondary injection processes.
It is already known, for example, from EP 1 132 607 A2 to carry out one or more pre-injection processes before the actual main injection process during one working cycle of the piston of an internal combustion engine. EP 1 138 921 A2, EP 1 081 365 A2 or DE 196 32 650 C1 describe further similar methods of injecting fuel.
The division of a fuel injection procedure into at least one pre-injection process and the main injection process achieves a reduction of the combustion chamber pressure gradient and therefore a slower pressure build-up in the combustion chamber. This leads to improved noise behavior of the internal combustion engine and a more accurate operation of the engine.
In this context, in particular in ranges with a low rotational speed, two pre-injection processes per working cycle of the piston are also frequently used, whereas no pre-injection process and merely one main injection process are frequently used in ranges of a high engine speed for reasons of improved performance yield. To this extent, one can speak of a variable number of pre-injection processes per main injection process. As it is also possible to carry out further injection processes of small amounts of fuel after the main fuel injection process, that is to say “post-injection processes”, pre-injection and post-injection are summarized by the term “secondary injections”.
In the transitional ranges where the change is made from an original number of secondary injection processes per working cycle or per main injection process to a changed number of secondary injection processes, problems frequently occur, however, with regard to the ability to regulate the injection process, as well as the torque and performance output, the exhaust-gas behavior, the rotational speed stability and the noise behavior of the internal combustion engine. In this connection, it is insignificant whether the number of secondary injection processes is increased or reduced during the method.
It is therefore the principal object of the present invention to provide a method for injecting fuel into the combustion chambers of an internal combustion engine, in which the transition between different numbers of secondary injection processes per associated main injection process does not lead to an impairment of the operation of the internal combustion engine, that is, to a method in which such transition proceeds harmoniously.